The invention relates to a process for the model-supported simulation of the coolant temperature in the case of a vehicle.
In the case of conventional vehicles, the coolant temperature must be known, for example, for the operation of the engine, the air-conditioning or heating system, or outside temperature measuring. For this purpose, the temperature of the coolant is sensed by at least one sensor.
In modern vehicles, the sensor emits a signal by way of a data bus to individual control devices in a motor vehicle. However, this data bus is often not operated before the terminal 15 "on" (condition corresponding to the ignition being "on"). However, the coolant temperature must be known before terminal 15 "on" for operating vehicle devices or for determining other quantities such as, for example, of the air-conditioning and heating system or of the outside temperature. For this reason, a second sensor is conventionally provided whose signal emits, already before terminal 15 "on" (thus before the ignition is switched on), a signal which corresponds to the coolant temperature. On the basis of this signal, the corresponding apparatuses, such as the air-conditioning system and the heating devices, can then be operated.
A disadvantage in this case are the additional costs for the use of a second sensor.
It is an object of the present invention to avoid using sensors for detecting the coolant temperature which are superfluous for cost and space reasons.
This object is achieved by a process for the model-supported simulation of the coolant temperature in the case of a vehicle. *The process detects the coolant temperature at the point in time of the switching-off of the driving engine, and continuously calculates the current coolant temperature while including vehicle-specific data using a temperature model. The object is further achieved by a process for the model-supported simulation of the cooling temperature in the case of a vehicle with the steps of detecting the coolant temperature at the point in time of the switching-off of the driving engine, and determining a point in time as of which a theoretically determined coolant temperature falls below a given limit value using vehicle-specific data and a temperature model.
Corresponding to the process according to the invention, the coolant temperature is sensed at the point in time of the switching off of the driving engine. Based on this value, a continuous calculation will then take place of the current coolant temperature including vehicle-specific data with the aid of a temperature model.
Such vehicle-specific data can, for example, be the heat transmission resistance of an engine to a virtual temperature sensor, the heat transmission resistance of such a virtual temperature sensor to the outside environment, a heat transmission resistance between the engine and the outside environment as well as corresponding heat capacities, that is, the heat capacity of the engine or of the engine system and/or of corresponding temperature sensors.
For many purposes, an approximate, for example linear, factoring into account of the corresponding heat transmission resistances or heat capacities will be sufficient. A linear transmission function could be implemented on a model of the first order. However, if additional influences, such as the wind, environmental influences, locations, etc., are also to be taken into account, preferably higher orders could be taken into account in the case of the models (transmission functions), that is, non-linear heat transmission resistances/capacities.
Preferably, the heat transmission resistance and/or capacity values are determined experimentally.
Conventionally, in the case of a vehicle, after the engine is switched off, the outside temperature sensing is discontinued and the temperature value is frozen at the last-sensed value. However, for the present invention, this will take place only if the temperature value changes upwardly. When the outside temperature value changes in the downward direction, no freezing will take place. The reason for this is that a control of the heating system, for example, takes place in accordance with the difference between the outside temperature and the coolant temperature and, particularly after the switching-off of the engine, the coolant temperature rises for a short time because of temperature coasting. When the coolant temperature then falls below a predetermined limit value after a certain time period, the lock for sensing the outside temperature is canceled and its value is indicated correspondingly.
As an alternative, in the case of another process according to the invention, the point in time is determined as of which a theoretically determined coolant temperature falls below a given limit value. This takes place by factoring into account vehicle-specific data and by using a temperature model. With the falling below of the theoretically determined limit value--as indicated above--a lock can be released again.
The point in time as to when the limit value is crossed can preferably be determined in that it is read out of a table in which specific operating and/or environmental conditions as well as vehicle-specific conditions are assigned to the corresponding points in time. In addition, estimated time constants as a function of the environment and of the vehicle type can also be stored in such tables.
Another embodiment consists of calculating the point in time by including operating, environmental and/or vehicle-specific conditions. Such a calculation is possible in an approximate manner, for example, by the formula EQU t.sub.w =-T ln (10/.DELTA.T),
wherein T is the coolant temperature at the point in time of the switching-off of the engine and .DELTA.T is the temperature difference between the coolant temperature and the temperature of the outside environment.